The study looked at the potential impacts of large-scale mining in the Bristol Bay and two other river watersheds, considering a potential open-pit mine producing 2-6.5 billion tonnes of ore and a 139-km transportation corridor:

Based on this mine scenario, we conclude that, at a minimum, mining at this scale would cause the loss of spawning and rearing habitat for multiple species of anadromous and resident fish. A mine footprint of this scale would likely result in the direct loss of 87.5 to 141.4 km of streams and 10.2 to 17.3 km2 of wetlands.

The report abstract notes that even if mining did not result in any accidents or failures, the mine "would result in significant impacts on fish populations in streams surrounding the mine site." Accidents or failures could include the release of contaminants or the catastrophic failure of a tailings dam.

The release of the report coincides with an announcement this week by Northern Dynasty stating that the Pebble Partnership is planning to spend $107 million to advance the mine in 2012, with the objective of achieving permitting by the end of this year.

The Pebble Mine is one of the largest undeveloped polymetallic mineral deposits left in the world.

According to a project website, the deposit hosts 55 billion pounds of copper, 76 million ounces of gold, 3.3 billion pounds of molybdenum, and quantities of silver, palladium and rhenium. Comparing the world's undeveloped gold deposits, Pebble ranks no. 1, dwarfing even Rio Tinto's Oyu Tolgoi project in Mongolia, which is ranked fourth at just over 40 million gold ounces.

So far the Pebble Partnership has invested about $500 million into the project, including about $150 million on studies.

The size of the proposed mine and its location near salmon-bearing streams has attracted considerable controversy and opposition from some quarters.

Last November, 81% of the Bristol Bay Native Corporation — the largest private landholder in southwest Alaska — rejected the mine on the basis that it will "unavoidably put at risk the 'fisheries and our Native way of life."

A month earlier, voters in the Lake and Peninsula Borough narrowly supported (by 34 votes) a ballot measure put forward by anti-Pebble activists that would restrict future development that affects more than one square mile of land within the 31,000 square mile borough.